** FILE ** In his Jan. 24, 2008 file photo, Environmental Protection Agency Administrator Stephen Johnson, is seen in Washington. A House committee on Friday, June 20, 2008, backed off a threatened contempt of Congress vote against the EPA chief after President Bush made a last-minute assertion of executive privilege over information the committee wants. (AP Photo/Dennis Cook, File)

Photo: Dennis Cook, AP

** FILE ** In his Jan. 24, 2008 file photo, Environmental...

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Sens. Barbara Boxer, D-Calif., speaks to reporters regarding the FAA Bill on Tuesday, May 6, 2008 on Capitol Hill in Washington. Major legislation to make the flying skies safer faltered in the Senate Tuesday; the vote was 49-42 to proceed with the Aviation Investment and Modernization Act, 11 short of the 60 needed. (AP Photo/Lauren Victoria Burke)

Four Senate Democrats called on EPA chief Stephen Johnson to resign Tuesday, alleging that he gave misleading testimony to Congress and repeatedly bowed to pressure from the White House to avoid regulating greenhouse gases.

The pressure on Johnson is part of an escalating battle between Democrats in Congress and the White House over climate change policy. Democrats are seizing on new evidence that Johnson overrode the opinions of Environmental Protection Agency scientists and reversed two of his own decisions at the request of the White House.

EPA spokesman Jonathan Shradar fired back at Boxer for what he called a political attack. "Administrator Johnson's record is one of aggressive, health protective environmental standards. Sen. Boxer's record is one of press conferences and political tirades," Shradar said.

Democrats insist that Johnson misled Congress when he testified before Boxer's committee Jan. 24 about his decision to reject California's effort to set the nation's toughest limits on emissions from vehicles. The EPA chief testified that he listened to all sides before deciding that California had failed to make its case.

"I made the decision. It was my decision. It was the right decision," Johnson said at the time.

But last week, a top Johnson aide contradicted his testimony. Former EPA deputy associate administrator Jason Burnett, who resigned last month in frustration with the administration's climate-change stance, testified that Johnson had initially supported granting at least a partial waiver after concluding that California met the legal criteria.

But Burnett said Johnson changed his stance when the White House made clear that President Bush opposed California setting its own fuel economy standards. "The administrator knew the president's preference for a single (national) standard," Burnett said.

Klobuchar said the testimony showed that Johnson not only overruled his own staff but also misled the public about who really made the decision. "If we can't trust the top EPA official to tell the truth to the American people, then he must go," she said.

The lawmakers also allege that Johnson yielded to White House influence in a recent EPA decision over whether climate change endangers human health. The decision was critical because if the agency had made such a finding, it would have been required to start regulating greenhouse gases.

In December, EPA officials sent an e-mail to the White House stating that Johnson supported the EPA staff's view that global warming threatens human health. "In sum, the Administrator is proposing to find that elevated levels of [greenhouse gas] concentrations may reasonably be anticipated to endanger public welfare," the document read.

The White House refused to open the e-mail and later asked EPA officials to retract it. When Johnson recently announced that EPA was starting a new rule-making process to determine whether climate change poses a health risk, he never mentioned this previous finding.

Boxer said she was frustrated that EPA officials have stonewalled congressional inquiries into those recent decisions. Johnson refused to testify at a Senate Judiciary Committee hearing this week about EPA's dealings with Congress. Last week, the White House released the e-mail with EPA's draft of the endangerment finding but would not allow senators to make copies. Lawmakers were allowed to read it only while being watched by two White House lawyers.

Boxer said the final straw was an e-mail sent to EPA staffers last month that directed them not to speak to the press, congressional investigators or to EPA's own inspector general, and to forward the inquiries to their superiors. Boxer said Johnson "has become a secretive and dangerous ally of polluters, and we cannot stand by and allow more damage to be done."

But the White House is standing behind Johnson. White House spokesman Trey Bohn said Johnson's critics are attacking him because they disagree with the administration's policies on energy and climate change.

"In every sense, administrator Johnson has cooperated fully with Congress, and the facts bear that out," Bohn said.